The Reliability and Validity of Isometric Midthigh Pull Measures Obtained from a Portable Isometric Dynamometer

The purpose of this investigation was to establish the reliability and concurrent validity of measures of peak and early force production obtained from a portable isometric dynamometer (PID). Twenty resistance trained males completed one familiarization and two isometric mid-thigh pull testing sessions separated by 48-72 hrs. During testing sessions data was simultaneously collected from the PID and force plates (FP) both sampling at a frequency of 1000 Hz. Measurements of peak force (PF) and force at 100 ms (Force100) and 200 ms (Force200) obtained from both the PID and the FP demonstrated acceptable reliability (ICC’s = 0.793-0.966; CV% = 2.7-9.2%). However, PF was significantly and meaningfully greater (P < 0.001; d = 1.00) 1.27% greater when obtained from the FP compared to the PID. In contrast, Force100 obtained from FP was significantly lower to that obtained from PID by 229% (P < 0.001; d =3.96). Similarly, Force200 obtained from FP was significantly lower to that obtained from PID by 38.87% (P < 0.001; d = 1.43). Whilst the measures of force production obtained from the PID was shown to have acceptable reliability they displayed questionable validity, particularly with respect to measures of early force production.